Case 349

History A 76-year-old man presented to the emergency department with a 1-month history of worsening binocular diplopia on left horizontal gaze, along with 1 week of progressive dysarthria and dizziness. Additionally, he had a chronic history of right-sided cervicobrachialgia related to degenerative disk disease, which had been improving with oral analgesia. The patient's past medical history included hypertension, dyslipidemia, insomnia, and hypothyroidism. He also had postpolio syndrome affecting the right lower limb. He reported no fever, chills, cough, shortness of breath, abdominal pain, or chest pain. There was no history of rash, intravenous drug use, immunosuppressive medication use, or documented congenital abnormalities. He reported no recent or recurrent bacterial or viral infections. At clinical examination, the patient appeared tired and had a decreased level of alertness. He was hypertensive (165/91 mm Hg) but had a normal body temperature. Other vital signs were unremarkable. Neurologic assessment revealed left abducens nerve palsy, right lower facial palsy, horizontal nystagmus during right eye adduction, and right lower limb paresis with ipsilateral patellar hyperreflexia. Brain MRI performed the day after admission showed imaging abnormalities (Figs 1-3). Laboratory testing showed an elevated C-reactive protein level (135 mg/L; upper limit of normal, 1 mg/L); other blood tests were within normal limits. Extensive additional diagnostic workup-including serologic testing for anti-aquaporin-4 antibody, anti-DNA antibody, lupus anticoagulant, antinuclear antibody, anti-cardiolipin antibody, and rheumatoid factor-yielded negative results. Lumbar puncture revealed a normal cerebrospinal fluid opening pressure (18 cm H₂O; upper limit of normal, 25 cm H₂O). The cerebrospinal fluid was clear, with a normal total nucleated cell count (3.75/mm³; reference range, 0-5/mm³), normal glucose level (53 mg/dL [2.9 mmol/L]; reference range, 50-77 mg/dL [2.8-4.3 mmol/L]), and elevated total protein level (750 mg/L; reference range, 100-450 mg/L). Cerebrospinal fluid oligoclonal bands were positive.